1. Field of the Invention
The present invention relates to a heater, more specifically, to a heater which is capable of exchanging heat between air sucked from the interior of a room and combustion heat generated during the combustion of a fuel such as gas or kerosene, with a very high level of efficiency.
2. Description of the Prior Art
An FF type warm air heater is conventionally known.
A known warm air heater of this type has a construction which can be outlined as follows: the heater is adapted to burn a fuel with air sucked from the exterior of the room and discharge air to the exterior of the room after the air has been used in the combustion; the heater is also adapted to perform heat exchange between air at a high temperature resulting from the combustion and air sucked from the interior of the room until the air at the high temperature is discharged to the exterior of the room, and forcibly supply the interior of the room with the air which has been subjected to heat exchange and thus had its temperature raised.
Such a conventional heater mainly comprises a combustion section, a ventilation section, a heat exchange section between the combustion and ventilation sections, and a frame body which accommodates these members.
The combustion section has a combustion chamber, a suction port for supplying fresh air from the exterior of the room to the inside of the combustion chamber by a suction fan, and an exhaust port communicating with the exterior of the room for discharging the air which has been used in the combustion to the exterior of the room. The heat exchange section is positioned between the combustion chamber and the exhaust port.
The ventilation section has a suction port disposed on one side of the frame body for sucking air from the interior of the room, a discharge port disposed on the other side of the frame body for discharging air to the interior of the room, and a ventilation fan disposed between the suction and discharge ports, so that the sucked air is forcibly subjected to heat exchange.
The heat exchange section is disposed between the combustion chamber and the exhaust port for providing heat exchange with air sucked from the interior of the room by the ventilation section. Air at high temperature resulting from the combustion passes through the heat exchange section, and, during the passage of the air, its temperature is reduced by a level corresponding to the energy used to raise the temperature of the air sucked from the interior of the room. Thereafter, the air which has had its temperature reduced is discharged to the exterior of the room.
The conventionally known heater has the advantage that it enables the room to be heated without causing any reduction in the freshness of the air within the room. The conventional heater, however, has the following disadvantages:
(1) Low Heat Exchange Efficiency
In the above-described conventional heater, air sucked from the interior of the room is subjected to heat exchange by the heat exchange section with heat generated by the combustion gases. If, however, it is attempted to increase the heat exchange efficiency by increasing the heat transfer area of the heat exchanger, there is a risk of moisture condensing in the heat exchanger. Such moisture condensation may result in corrosion of the heat exchanger. Accordingly, it has been necessary to set the heat exchange efficiency of a conventional heater to within a range which is low enough to prevent moisture condensation, and it has been impossible to increase the heat exchange efficiency beyond this range.
(2) Large Heat Exchanger Volume
The efficiency of the heat exchange in the heat exchange section between air at high a temperature provided by the combustion gases and air at a low temperature sucked from the interior of the room can be increased by increasing the heat transfer area of the heat exchanger. This increase in the transfer area, however, causes an increase in the resistance to the flow of air in the flow passages caused by the ventilation fan. In order to cope with this problem, it is common practice to enlarge the cross-section of the flow passages. Since the heat exchanger per se must have an increased volume to provide an increased heat exchange efficiency, these arrangements made the overall structure of the heater large.
(3) Drying of Air within the Room
Since the conventional heater is adapted to discharge all the air which has been used in the combustion, the moisture in that air is also discharged after it has been vaporized during the combustion. This arrangement, therefore, abnormally dries the interior of the room as it is heated by the heater.